As of Saturday afternoon, the fire had burned more than 20,000 acres with 763 people working on containing it, even as the heat plagued the effort.

As the hot sun beats down, ground temperatures rise and plants start to dry out, creating more fuel for the fire.

Even in places where the fire had been put out, the chance of reigniting increases on hot days, Mills Canyon fire incident manager Nathan Rabe said on Saturday at a media briefing near the incident-command post at Entiat High School in Chelan County.

Tents cover the Entiat school’s athletic field, where the firefighters have set up camp. The school gym has been converted to sleeping quarters for most of the night-shift workers. The windows have been darkened to help them adjust to sleeping through the day.

The sleeping areas for the firefighters are strictly off-limits, Rabe said. It’s hard enough to keep them rested and hydrated.

“Heat is a huge issue for us,” he said.

But heat also is just something you have to acclimate to as a firefighter, said Erin Kimsey, a hot-shot crew member who left Oregon Tuesday night to come fight the fire.

Kimsey said it is important to stay hydrated, but a lot of firefighters forget to eat as well. She said it is easy for firefighters to get focused on the mission and forget about taking care of themselves.

Kimsey works the night shift, and making that adjustment can be tough.

“The first (night) shift is always the hardest,” Kimsey said.

But Kimsey also thinks her crew is lucky for pulling that shift — the heat is not as intense at night.

The National Weather Service forecasts temperatures above 100 degrees near Entiat for the next five days.

While working and wearing all of their equipment, temperatures will feel 10 to 15 degrees hotter, said Adrian Fernandez, Mills Canyon fire medical-unit leader.

Firefighters lose nearly a liter of fluid every hour while working, Fernandez said.

“This is not about being macho; this is not about being thirsty,” Fernandez said. “This is about taking care of yourself and replenishing fluids.”

To combat the loss of liquids, Fernandez said firefighters are trained to drink one liter every hour. It has to be more than just water, Fernandez said, because it is important for fire crews to get electrolytes into their bodies. He said most firefighters mix water and Gatorade together.

Fernandez said the majority of the crews working the Mills Canyon fire are experienced hot-shot crews and hydrate properly. There have been a few cases of heat rash, but no cases of heat exhaustion or heat stroke yet.

“Our crews work 14 to 21 days in a row,” Rabe said. “We schedule our days for 12 hours, but typically they are working 14-hour days. ”

Firefighters are taught not just to look out for themselves but for others on the crew. Fernandez said heat stroke and heat exhaustion can cause the brain to not work properly and it is hard for some individuals to realize they are not feeling well.

“When you get sick enough you’re not even helping yourself, somebody else has to recognize it,” Fernandez said.

The fire, which as of Saturday was 22 percent contained, is still growing and very dangerous. The focus for the crews on Saturday was to keep it from spreading to populated areas.

An immediate evacuation level has been recommended for occupants of about 42 buildings, but deputy incident manager Richard Andring said he does not know of anyone who has actually left yet. The Red Cross is operating a shelter for displaced people in Wenatchee.

Some things have gone well for the firefighting effort though. Rabe said the weather was more of an issue Wednesday and Thursday, when 30- to 35-mph winds spread the fire. “We just have our normal winds,” Rabe said. “The weather has cooperated with what we are trying to do.”

On Sunday morning, a new management team will take over. Because of the complexity and possibility of growth, the Pacific Northwest Management Team 3 will take the reins of the Mills Canyon fire.

The new command will not change the ground operations, Rabe said; the change is just to bring in people who have managed fires of this size before.